1. Field of the invention
This invention relates to electrical circuits which change the difference in temperature between two points into differences in magnitude and direction of voltage and to circuits which contain electrical equipment which is sensitive to changes in magnitude and direction of voltage.
2. Description of the related art
The prior art is aware of electrical devices which measure temperatures at two separated points with thermistors and which change any difference in temperature to an electrical current which operates to change a condition. Thus, U.S. Pat. No. 3,931,620 to Wellman, Jr., et al describes an alarm system which contains a bridge network containing a thermistor and a transistor. U.S. Pat. No. 5,655,379 to Jaster et al describes a refrigerant control device which comprises a pair of thermistors. This control device is operated in dependence upon the current generated due to a difference or equality of temperatures which, in turn, is dependent upon whether one thermistor is in contact with the refrigerant liquid and one thermistor is in contact with the refrigerant vapor or whether both thermistors are in contact with the refrigerant vapor. In order for the Jaster et al circuit to be operative, the thermistors must be inside the phase separator of a refrigeration system, thus making retrofitting and field installation difficult and expensive. The Jaster et al circuit is not a true resistance type bridge circuit. Also, in the Jaster et al device, the voltage of current flow in a single direction may be changed, but reversal of current direction is not possible.